In the field of offshore pipelay, it is known to form a pipeline by assembling a pipeline sections on a vessel and deploying the assembled pipeline from the vessel to the seabed. Typically, a pipelay operation will be carried out from a dedicated pipelay vessel. The pipelay vessel stores and transports a number of pipeline sections, which are joined together on an assembly line or firing line and launched from the vessel. Where the pipeline is formed on the vessel in a generally vertical orientation, the system is referred to as a J-lay system. Where the pipeline is formed in a generally horizontal orientation, the pipeline operation is referred to as S-lay system. J-lay or S-lay pipelay systems include pre-assembly lines in which individual pipeline sections are joined into a multiple length pipeline section, which is then joined to the main pipeline on an assembly line.
One conventional method of joining pipe sections is welding. Welding methods are reliable and well-understood, but are time consuming and expensive due to the time required to complete and inspect each weld. To mitigate this, welding pipelay systems typically use a pre-assembly line in which multiple welds are performed concurrently at weld stations positioned at axially separated locations. The vessel therefore requires a large deck to accommodate the length of the pre-assembly line which is required to make the process more efficient.
WO 2011/037459 describes an offshore pipelay vessel used in S-lay installation operations. The vessel comprises a pre-assembly line for forming multiple length pipe sections, an inspection station and a main assembly line. A conveyor system transports single pipe sections or multiple pipe sections from a pipe elevator. The system of WO 2011/037459 is configured such that the assembly line may receive single pipe sections directly from the pipe elevator, or multiple pipeline sections via the pre-assembly line and inspection station.
The vessel of WO 2011/037459 is stated to provide efficient and versatile handling of pipe sections. However, the configuration described is only suitable for a dedicated pipelay vessel due to the complexity of the conveyor system.
An alternative pipe connection technique is a mechanical interference fit pipe-joining method. Mechanical interference fit methods have the advantage that each joint can be made up in a fraction of the time required to create a weld joint. Examples of mechanical interference fit pipe systems include those described in U.S. Pat. Nos. 4,095,825, 4,064,619, 4,120,083, and 4,091,648 and marketed by Zap-Lok Pipeline Systems Inc. as the ZAP-LOK pipeline system.
Mechanical interference fit systems are able to provide benefits in offshore pipelay installation methods by eliminating the requirement for x-ray inspection, eliminating field joint coatings, increasing corrosion protection, and ultimately increasing construction speed. However, existing pipelay vessels are not configured to utilise the benefits of mechanical interference fit pipelay technologies. Current methods of configuring existing pipelay vessels for alternative connection technologies are not financially viable.
It is therefore amongst the aims and objects of the invention to provide a pipelay system which offers benefits in offshore applications of mechanical interference fit pipelay technologies.
More generally, it is amongst the aims and objects of the invention to provide a pipelay system, apparatus and/or method of use which overcomes one or more deficiencies or drawbacks associated with conventional pipelay systems.
It is amongst the aims of at least one aspect of the invention to provide a pipelay system which is modular; which may be readily transported onshore and installed on a vessel; and/or which is suitable for application to a range of vessel types and sizes.
Other aims and objects of the invention will become apparent from reading the following description.